取消的任务也显示为已完成

Question

我正在研究异步等待和取消，以便对此事有更多了解。为此，我制作了以下控制台应用程序：

using System;
using System.Threading;
using System.Threading.Tasks;

namespace AsyncTest
{
    class Program
    {
        private static CancellationTokenSource _cancellationTokenSource;
        private static CancellationToken _cancellationToken;

        static void Main(string[] args)
        {
            Console.CancelKeyPress += myHandler;

            _cancellationTokenSource = new CancellationTokenSource();
            _cancellationToken = _cancellationTokenSource.Token;

            var task = DoWorkAsync(_cancellationToken).ContinueWith(ContinueMethod);
            task.Wait();

            Console.ReadLine();
        }

        protected static void myHandler(object sender, ConsoleCancelEventArgs args)
        {
            if (_cancellationToken.CanBeCanceled)
            {
                _cancellationTokenSource.Cancel();
            }
            args.Cancel = true;
        }

        static void ContinueMethod(Task task)
        {
            if (task.IsCanceled)
            {
                Console.WriteLine("The task was canceled");
            }

            if (task.IsCompleted)
            {
                Console.WriteLine("The task completed successfully");
            }

            if (task.IsFaulted)
            {
                if (task.Exception != null)
                {
                    var exceptions = task.Exception.Flatten().InnerExceptions;
                    foreach (var exception in exceptions)
                    {
                        Console.WriteLine(exception.Message);
                    }
                }
                Console.WriteLine("The task failed");
            }
        }

        static async Task DoWorkAsync(CancellationToken cancellationToken)
        {
            await Task.Run(() => DoWork(cancellationToken), cancellationToken);
        }

        static void DoWork(CancellationToken cancellationToken)
        {
            cancellationToken.ThrowIfCancellationRequested();

            Console.WriteLine("DoWork() is started");

            // Uncomment the following line of code to put the task in a 'faulted' state
            //throw new Exception();

            for (var count = 0; count < 10; count++)
            {
                if (cancellationToken.IsCancellationRequested)
                {
                    Console.WriteLine("Get a cancelation request");
                    cancellationToken.ThrowIfCancellationRequested();
                }
                else
                {
                    Thread.Sleep(500);
                    Console.WriteLine("Count : " + count);
                }
            }
            Console.WriteLine("DoWork() is finished");
        }
    }
}

当我让应用程序完成时，我正确地收到了 "The task completed successfully" 消息。

现在，当我按下 CTRL+C 时，这会触发对已启动任务的取消（请参阅 myHandler 中的拦截），我会正确地收到 "The task was canceled" 消息。但我也收到 "The task completed successfully" 消息。我没想到任务也会显示为已完成，因为我取消了它。如果我取消注释 DoWork() 方法中的 throw new Exception(); 行，我会正确地收到 "The task failed" 消息，还有 "The task completed successfully" 消息。我的假设错了吗？这是设计好的吗？还是我完全错过了其他东西？

我当然可以通过添加如下额外检查来解决这个问题：

if (task.IsCompleted && !task.IsCanceled)
{
    Console.WriteLine("The task completed successfully");
}

但我不确定这是不是正确的方法，或者我的程序中是否有其他原因导致了此完成状态。

提前感谢您对此事的输入and/or澄清。

Answer 1

Task.IsCompleted 的文档说

IsCompleted will return true when the task is in one of the three final states: RanToCompletion, Faulted, or Canceled.

所以 IsCompleted 至少告诉您任务不再是运行。它不表示任务是成功完成、失败还是被取消。

Answer 2

使用Task.IsCompletedSuccessFully

取消的任务也显示为已完成

Canceled task also appears as completed

c#

task-parallel-library

cancellation